ERBB2 and neoplasm: Trastuzumab is a humanized IgG1 monoclonal antibody, which binds to the extracellular regions of HER2 and inhibits the formation of homodimer of HER2 and heterodimer of HER2-HER3, thus blocking the activation of downstream signaling pathways (such as PI3K/AKT) and restricting tumor cell growth [14].